1. Field of the Invention
The present invention relates to an optical pickup device in which a photodetector does not deviate from its proper position, even when undergoing a significant change in temperature.
2. Description of the Related Art
FIG. 6 is an explanatory diagram showing an example of an optical pickup device, with FIG. 7 being an enlarged view showing the main section of the optical pickup device.
A current is fed from an LDD (laser diode driver) 510 (shown in FIG. 6) to an LD (laser diode) 520, to thereby cause the LD 520 to output laser light. Here, the LD is an example component for emitting laser light and is also referred to as a light emitting element. The LDD 510 is a laser driving circuit which activates and causes the LD 520 to emit laser light. A current fed from the laser diode driver (LDD) 510 to the laser diode (LD) 520 causes the laser diode (LD) 520 to emit laser light, and, by means of the laser light, data recording onto a disc 700 or reading of data recorded on the disc 700 is performed.
The laser light output from the LD 520 is irradiated via a diffraction grating 530, an intermediate lens 540, a half mirror 550, and an object lens 560 onto the disc 700. A portion of the laser light reflected from the disc 700 is applied to a PDIC (photo diode IC) 570. The PDIC 570 transforms incident light into an electrical signal to activate a servo mechanism (not illustrated) for a lens holder (not illustrated) in an optical pickup device 501. The PDIC, which detects incident light, is also referred to as a photodetector. A servo denotes a mechanism to automatically correct and control a state of a control target based on a result of detecting the state of the control target and comparing the measured state with a predetermined reference value.
Further, a portion of the laser light output from the LD 520 enters into a FMD (front monitor diode) 580, for monitoring the laser light emitted from the laser diode to provide feedback for controlling the laser diode.
The LDD 510, the LD 520, the diffraction grating 530, the intermediate lens 540, the half mirror 550, the object lens 560, the PDIC 570, and the FMD 580 are installed in a housing 502 shown in FIG. 7. The LDD 510, the LD 520, the PDIC 570, and the FMD 580 shown in FIG. 6 are electrically and physically connected to an FPC (flexible printed circuit) 505. In the FPC 505, a plurality of circuit conductors are printed on an insulation sheet; a metal foil, such as copper foil, for example, is disposed on the insulation sheet; and a protective layer is provided on the sheet. The optical pickup device 501 comprises the above-described various components. Although the optical pickup device 501 includes components other than those illustrated in the drawing, the additional components are not depicted in FIG. 6 in order to simplify the diagram.
The optical pickup device 501 is used to read or record data, such as information, on a medium. As such a medium, there has been provided a wide variety of optical discs including a read-only optical disc, such as a CD-ROM, DVD-ROM, or the like, a write-once optical disc, such as a CD-R, DVD±R, or the like, and an writable/erasable or rewritable optical disc, such as a CD-RW, a DVD±RW, a DVD-RAM, or the like.
CD is an abbreviation for “compact disc”, and DVD is an abbreviation for “digital versatile disc” or “digital video disc”. Further, ROM in “CD-ROM” and “DVD-ROM” is an abbreviation for “read only memory”, and a CD-ROM and a DVD-ROM are read only discs. In addition, R in “CD-R” and “DVD±R” stands for “Recordable”, and a CD-R and a DVD±R are writable. RW in “CD-RW” and “DVD±RW” stands for “Re-Writable”, and a CD-RW and a DVD±RW are rewritable. Further, DVD-RAM which is an abbreviation for “digital versatile disc random access memory” is readable, writable, and erasable.
The optical pickup device 501 is defined as a unit used for reading data recorded on the above-described various optical discs and recording data on one or more of the various writable or rewritable optical discs.
When the current passes through the LDD 510 causing the LD 520 to emit laser light, heat is generated in the LD 520. Because the wavelength of laser oscillation in the LD 520 is dependent on the temperature upon emission of the laser light from the LD 520, significant variations in the temperature of the LD 520 result in variations in the wavelength of the laser light emitted from the LD 520. Further, because the LDD 510 also generates heat when the laser light is emitted from the LD 520 by the passage of a current fed from the LDD 510 to the LD 520, both the LDD 510 and the LD 520 are regarded as major heat sources in the optical pickup device 501.
As shown in FIG. 7, the PDIC 570 mounted on a FPC 505 is electrically connected to the FPC 505 by means of soldering. The FPC 505 is attached to an aluminum plate 503 which is bonded to a housing 502 using an adhesive 504. In FIG. 7, the solid black regions represent the adhesive 504. In this manner, the PDIC 570 is mounted, via the FPC 505 and the aluminum plate 503, to the housing 505.
In addition to the above-described technology, a method of securely fixing an optical pickup to a plate equipped with an electronic component is disclosed in which the plate equipped with an electronic component such as a photodiode is properly positioned even under adverse conditions of temperature changes, vibrations, or the like, while still reducing manufacturing costs.
However, there has been a concern regarding the optical pickup device 501 shown in FIG. 7 that if the temperature of the optical pickup device 501 greatly changes, installation position of the PDIC 570 will be shifted relative to the housing 502.
As described above, the PDIC 570 is placed on the housing 502 via the FPC 505 and the aluminum plate 503 and attached to the housing 502 by means of the adhesive 504 applied to a junction between the housing 502 and the aluminum plate 503 having the PDIC 570 and the FPC 505. Because, with such a configuration, any increase in temperature of the optical pickup device 501 causes all components, such as, for example, the housing 502, the aluminum plate 503, the adhesive 504, the FPC 505, and the PDIC 570, to expand and the solder connecting the FPC 505 and the PDIC 570 or the like to soften, positional deviations in each component are possible, and common.
Although the amount of positional deviation for each of the components is generally considered trivial, any positional error in the mounting of the PDIC 570 (photodetector) relative to the housing 502 will be increased when the amount of positional deviation for each of the component is accumulated. The increased mounting error of the PDIC 570 (photodetector) relative to the housing 502 leads to a change in focus of light incident upon the PDIC 570 (photo detector shown in FIG. 6). Because such a change develops a greater likelihood of unstable operation of the servo mechanism in the optical pickup device 501, there has been concern that precise operation of the servo mechanism cannot be assured.